1. Field of the Invention
This invention relates to a control for refrigerating or air-conditioning units and, more specifically, to a device for detecting either one of the degrees of superheating and supercooling to control a condenser fan or the like.
2. Prior Art
As disclosed in Japanese Utility Model Application Laid-Open SHO 57(1982)-79010, for instance, there is known a control for regulating the speed of rotation of a condenser fan in a refrigerating or air-conditioning unit, which is designed to detect the temperature or pressure of a coolant on the high-pressure side of a refrigerating cycle and thereby vary the terminal voltage of the motor for the condenser fan based on the thus detected signal for the purpose of energy savings and noise reduction.
However, the degree of supercooling correlating with both the temperature and pressure of the coolant on the high-pressure side should be detected to make a determination of what surplus is left in the air-cooling capacity. In the prior art, only either the temperature or the pressure has been detected to control the speed of rotation of the condenser fan. For that reason, there have problems that the air-cooling capacity is not balanced with the speed of rotation of the condenser fan, so that the condenser fan is rotated at high speeds resulting in waste of energy, or at too low speeds resulting in insufficient dissipation of heat from the condenser. A solution to these problems may be provided, if both the temperature and pressure sensors disclosed in the aforesaid publication are arranged in the high-pressure coolant passage to make it possible to calculate the degree supercooling from the outputs thereof. However, this would lead to an increase in the number of the parts involved, make the control complicated and cause an increase in the price.